The purpose of this investigation is to solubilize, purify, isolate and characterize tumor rejection antigens from 5-bromodeoxyuridine -grown mouse melanoma cells and to isolate and characterize plasma membranes from the treated and untreated cells. The treated cells are non-tumorigenic and are highly immunogenic when inoculated into adult C57Bl/6J mice, protecting them against tumor formation when subsequently challenged with the untreated tumorigenic non-immunogenic parental melanoma line. A crude membrane fraction will be prepared first, then a crude soluble fraction and the latter fraction purified by chromatography. Each fraction will be monitored for tumor rejection in vivo to be sure the active antigen is contained therein. Isolated plasma membranes will be inoculated into mice and the degree of protection against subsequent challenge similarly determined. If all preceding procedures are successful, the same protocols will be used with a mouse mammary adenocarcinoma we have adapted for culture. The ultimate aim of these studies is to use them as model systems forming a basis for safe immunization of melanoma and breast cancer patients after removal of their primary tumors. The biological assay used in the animal model systems should provide strong validation that the fractions obtained are those inducing tumor immunity.